Variable valve gear

ABSTRACT

A variable valve gear particularly for internal combustion engines, in which a control cam of a camshaft acts, by way of pair of swivellably coupled levers, to a valve to produce an adjustment of the valve stroke. The valve stoke can vary continuously from a maximum lift to zero lift while the valve clearance can remain unchanged.

[0001] The invention provides a variable valve gear particularly forinternal combustion engines, in which a control cam of a camshaft acts,by way of a pair of swivellably coupled levers, to a valve to produce anadjustment of the valve stroke. The valve stroke can vary continuouslyfrom a maximum value to zero while the valve clearance is heldunchanged.

[0002] In the prior art several variable valve gear mechanisms aredescribed. The objective is always the adjustment, continuous ifpossible, of valve operation, as regards valve stroke and valve timing,so that the breathing of the engine being the best for the particularoperational conditions. Some of the most relevant patents are: U.S. Pat.Nos. 5,899,180, 5,373,818, 5,205,247, 5,732,669, 5,056,476, 6,145,485,6,032,624, 4,502,426, 5,937,809, 6,029,618, 5,996,540, 5,988,125,6,055,949, 6,123,053, 6,019,076, 5,003,939 and 5,365,895

[0003] The advantages of a continuously variable valve gear are known tothose relative to the art. Some of the side effects are the extra cost,the lower revs limit, the involvement of strong springs, thecomplication in assembly and service, the extra height, the frictionloss, the noise.

[0004] Achieving slight valve strokes allows for elimination of thethrottle valve resulting in reduced consumption, reduced pollution andbetter performance, especially at partial loads, without compromise inpower output.

[0005] In the present invention the additional components are fewer, insome realizations two additional pieces per valve, plus a control shaftper row of valves, they can be light, especially those ones bound tomove quickly, they can be small in dimensions, so the engine's heightcan be low, they do not need special construction accuracy, therestoring force, for secure contact of cam follower to control cam, isgenerated basically by the valve spring, so additional strong restoringsprings are not a necessity, the resulting thrust force to the valve'sbucket lifter or to the valve's rocker arm is small, especially at highvalve strokes and high revs, the throttle in the induction system isnecessary no more since the stroke of the valve can vary from a maximumto zero, the friction is small.

[0006] The closest prior art is the U.S. Pat. No. 5,899,180 of Fischer,where the rotation of a control shaft, which serves a row of valves,changes the valve timing and stroke in a continuous manner. In thatpatent an arm has a roller, at one end, which rolls on a control cam ofa camshaft. The arm is rotatably supported, at its other end, about anaxis. As this axis moves along a path, due to the rotation of thecontrol shaft, the resulting stroke/timing of the valve is changingcontinuously. The roller moves along a circular arc. As this circulararc changes position relative to the circular arc contact surface of theroller on the rocker arm, the valve stroke and the valve timing changes.When the two arcs are “vertical” to each other, the valve stroke islong. When the two arcs are “parallel” the resulting valve stroke issmall. So, by rotating the control shaft, the stroke/timing of a row ofvalves is controlled.

[0007] In the present invention there is also a control shaft. Thiscontrol shaft can rotate about a, fixed to the engine, axis. For eachvalve in a row there are two levers, the valve lever and the controllever, swivellably coupled at one end. The control lever is rotatablysupported, at its other end, to the control shaft to rotate about amovable axis, like the arm with the roller in U.S. Pat. No. 5,899,180.The valve lever is swivellably coupled, at its other end, to the valve'srocker arm or to the valve's bucket lifter, that is to the valvedisplacing device. The cam follower is pushed by the control cam of thecamshaft, forcing the swivel joint coupling the control lever and thevalve lever to oscillate along an arc whose center is the movable axison the control shaft. The swivel joint, coupling the valve lever and thevalve's rocker arm or valve's bucket lifter, can move also along a path,circular in case of a rocker arm and linear in case of a bucket lifter.Depending on the relative position of the two paths, that one of theswivel joint coupling the control lever and the valve lever, and thatone of the swivel joint coupling the valve lever and the rocker arm orbucket lifter, the stroke of the valve changes continuously from amaximum to zero. The more “parallel” the two paths, the longer the valvestroke.

[0008] By selecting the effective lengths of control and valve levers,and by selecting the position of the rotation axis of the control shaft,constant valve clearance and continuously adjusted valve stroke, from amaximum value to zero, are achievable.

[0009] To secure contact of the cam follower to the control cam,particularly at short and very short valve strokes, an additional springelement can be inserted to assist this contact. In case of long valvestrokes the necessary restoring force comes from the valve spring, sothe spring element mentioned can stay inactive.

[0010] The system described in this patent in combination with somevariable valve timing system provides a completely controlled variablevalve gear system.

[0011]FIG. 1 shows a realization of the proposed variable valve gear.

[0012]FIG. 2 shows a disassembly of the mechanism of FIG. 1.

[0013]FIG. 3 shows the assembly and interconnection of the variousconstituents of FIG. 1.

[0014]FIG. 4 shows, from various points of view, the main constituentsof the 40 mechanism of FIG. 1.

[0015]FIG. 5 shows the mechanism of FIG. 1 for two angles of thecamshaft, adjusted for long valve stroke.

[0016]FIG. 6 shows the mechanism of FIG. 1 for two angles of thecamshaft, adjusted for an intermediate valve stroke.

[0017]FIG. 7 shows the mechanism of FIG. 1 for two angles of thecamshaft, adjusted for a very short or zero valve stroke.

[0018]FIG. 8 shows a temporal course of the operation of the mechanismof FIG. 1. In the upper row the mechanism is adjusted for long valvestroke, in the intermediate row the mechanism is adjusted for mediumvalve stroke and in the lower row the mechanism is adjusted for shortvalve stroke. The five stages shown in each row correspond to 180degrees total rotation of the camshaft, of 45 degrees steps.

[0019]FIG. 9 shows in sectional view what is shown in FIG. 8.

[0020]FIG. 10 shows a row of 8 valves controlled by a common controlshaft. They could, for instance, be the intake or the exhaust valves ofa four in line, sixteen valve, four cycle typical engine. The controlshaft or adjusting device is shown alone at left, from three differentpoints of view. In the third, from right, assembly the control shaft isrotated to give long valve stroke. In the second, from right, assemblythe control shaft or adjusting device is rotated to give a medium valvestroke. In the right assembly the control shaft or adjusting device isrotated for zero valve stroke.

[0021]FIG. 11 shows, from another point of view, what is shown in FIG.10.

[0022]FIG. 12 shows the assembly of FIG. 10 and 11 with the valves andthe valve bucket lifters removed, for better understanding. Here theyare shown the valve levers, the control levers, the common controlshaft, or adjusting device, and the camshaft.

[0023]FIG. 13 shows another realization. Here the cam follower is aroller rotatably supported to valve lever either to control lever. Therotation axis of the control lever is in a position, on the path drawnwith dashed dot line, for zero valve stroke. The mechanism is shown fortwo different angles of the camshaft.

[0024] In FIGS. 14, 15 and 16 it is shown the mechanism of FIG. 13, forthree other conditions of the adjusting device. In FIG. 14 the valvestroke is very short, in FIG. 15 the valve stroke is medium and in FIG.16 the valve stroke is long. The operation of the mechanism is similar,for the rest, to the mechanism of FIG. 1.

[0025] In FIG. 17 and 18 it is shown the mechanisms of FIGS. 13 to 16from other points of view.

[0026]FIG. 19 shows another realization of the present invention, fortwo angles of the camshaft. Here the displacing valve mechanism is arocker arm. The valve lever is swivellably coupled to the rocker arm,with the swivel joint being a cylindrical surface, at the end of thevalve lever, rotating in a corresponding cylindrical journal formed onthe rocker arm. Another difference from the previous mechanisms is thatthe cam follower is mounted on the valve lever. The shape of the camfollower is a plane surface but it could also be any other shape, as itis secured to the valve lever. Even so the clearance can remainconstant, no matter what is the condition of the control shaft, and thevalve stroke can change from a maximum to zero.

[0027]FIG. 20 shows the mechanism of FIG. 19 adjusted to offer a shortervalve stroke.

[0028] In FIGS. 21 and 22 they are shown the mechanisms of FIGS. 19 and20 correspondingly, in sectional views.

[0029] In FIG. 23 they are shown, from other points of view, themechanisms shown in FIGS. 19 to 22.

[0030]FIG. 24 shows a realization of the present invention with anadditional spring member for providing the necessary restoring force toassist the contact of the cam follower to the control cam, at shortvalve strokes. The mechanisms shown are exactly the mechanisms shown inFIGS. 5, 6 and 7 with the control shaft removed for clarity, and withthe addition of a spring member. The spring member comprises a springinside a case secured to the engine casing, not shown, and a stem. Thespring pushes linearly the stem. At long valve strokes the spring andthe stem are idle at their outmost position. For short valve strokes thestem comes in contact to the control lever, offering the necessaryrestoring force to secure the contact of the cam follower to the controlcam. For short valve strokes the restoring force, from the springmember, is added to the restoring force from the valve spring. Only atzero valve stroke all the restoring force is generated by the additionalspring member. If zero valve stroke is not used at all, and if the shortvalve strokes are only for low revs, an additional spring member is notnecessary.

[0031]FIG. 25 shows the mechanisms of FIG. 24 from another point ofview.

[0032] Referring to the mechanism shown in FIGS. 1 to 12, 1 is thecamshaft, 2 is a control cam mounted on said camshaft 1, 3 is a camfollower having a cylindrical shape and being mounted to the controllever 8. Said control lever 8 is rotatably supported at its end 17 to acontrol shaft 7, to rotate about an axis 9 of the control shaft 7. Thecontrol shaft 7 is rotatably supported to the engine frame, not shown,to rotate about a fixed to said engine axis 10. The control lever 8 isswivellably coupled, at its other end 11, to the valve lever 6. Theswivel joint coupling the control lever 8 and the valve lever 6comprises a spherical surface 12 at the end of the valve lever 6,inserted into a corresponding spherical cavity 11 of the control lever8. At the other end the valve lever 6 is swivellably coupled to thebucket lifter 5, or valve displacing device 5, of the valve 4. Theswivel joint coupling the valve lever 6 and the bucket lifter 5 iscomprises a spherical surface 13 at the end of the valve lever 6,inserted into a corresponding spherical cavity 18 of the bucket lifter.The valve 4 has a corresponding valve seat 14 to rest when it is closed.The effective length of the control lever 8, the effective length of thevalve lever 6 and the distance from the axis 10 to the axis 9 are allselected to be substantially equal. The location of the control shaft 7,or adjusting device 7, is selected so that the axis 10 passessubstantially through the center of the swivel joint coupling controllever 8 and valve lever 6, when the valve 4 is closed. As the camshaft 1rotates, the cam follower 3 is forced to perform a motion. The bearing16 on the adjusting device 7, in cooperation with the end 17 of thecontrol lever 8, allows to the control lever 8 just an angulardisplacement about the axis 9 of the adjusting device 7. Through the twoswivel joints, 11 to 12 and 13 to 18, the valve lever is pushed, at theend 12, from the control lever 8, and is pushing, at the end 13, thebucket lifter 5 which can move only linearly, so the rotation of thecontrol cam 2 is translated to angular oscillation of the control lever8 and then, by means of the valve lever 6, to linear oscillation of thebucket lifter 5 and valve 4. To change the valve stroke it suffices torotate, about the axis 10, the control shaft 7. In case the axis 9 ofthe adjusting device 7 is displaced to pass through the center of theswivel joint coupling valve lever 6 and bucket lifter 5, the stroke ofthe valve 4 becomes zero. With the mechanism proposed can be achievedboth, substantially constant valve clearance and ability for valvestrokes continuously variable from a maximum to zero.

[0033] The longer the valve stroke, the heavier the inertia loads.However at the long valve strokes is where the valve lever 6 remainsalmost parallel to the valve stem, FIG. 8 upper row, giving slighterthrust load to the bucket lifter 5. The restoring force, for securingthe contact of the cam follower to the control cam, can be generated bythe valve spring. If very short or even zero valve strokes are wanted,an additional spring could be located to provide the necessary force forholding in contact the cam follower 3 and the control cam 2, as shown inFIGS. 24 and 25. This spring can remain, as shown in FIGS. 24 and 25,completely idle at medium and long valve stroke operation.

[0034] In FIG. 3 it is shown the way for assembling the control lever 8to the control shaft 7, or adjusting device 7. As the rotation angle ofthe control lever 8 about the axis 9 of the control shaft is limited,there is no need for 360 degrees bearing 16 and pin 17. In the wayshown, for each valve in a row, just a control lever and a valve leversuffice. And for the whole row of valves it is needed only one commoncontrol shaft. The spherical swivel joints are not a necessity. Theycould also be cylindrical etc.

[0035] In case the effective lengths of control lever and valve lever,as well as the distance from 9 to 10 axis are not equal, again themechanism works but, depending on the selected lengths and the locationof the axis 10, the clearance of the valve may not be constant, and theavailable valve strokes may not include very short values.

[0036] The bucket lifter 5 can obviously have some hydrauliccompensation element inside.

[0037] The operation principle, for the mechanism shown in FIGS. 13 to18, is similar. The cam follower is a roller properly mounted to thecontrol and valve levers. The adjusting mechanism is not shown, but withdash dot line is shown the path of the axis 9. The swivel joints aremade with pins, one for the interconnection between the bucket lifter 5and the valve lever 6, and one for the interconnection between the valvelever 6 and the control lever 8.

[0038] The mechanism shown in FIGS. 19 to 23 is a similar one. Here thevalve displacing device 5 is a rocker arm. The swivel joint coupling thevalve lever 6 and the rocker arm 5 comprises a cylindrical surface atthe end of the valve lever 6, cooperating with a corresponding cavity ofcylindrical form of the rocker arm. The cam follower has not acylindrical shape, nevertheless the valve clearance can be constant andthe valve stroke can continuously vary from a maximum to zero. The formof the cam is not necessarily plane or cylindrical.

[0039] If it is desirable to be changed slightly the valve clearance,depending on the valve stroke, the shape of the cam follower could bemodified or a small offset from the theoretically perfect position ofthe axis 10 could be applied, or slightly different effective lengths,of control and valve levers, could be used.

[0040] In case of bevel or conical control cams, the previous could alsobe applied with some small modifications, obvious to the relevant of theart.

[0041] In case that different adjustment for the various valves in a rowis wanted, the adjustment mechanism could be designed to be able todisplace the axis 9 of each valve independently.

[0042] Although the invention has been described and illustrated indetail, it is to be clearly understood that the same is by way ofillustration and example, and is not to be taken by way of limitation.The spirit and scope of the present invention are to be limited only bythe terms of the appended claims.

What is claimed is:
 1. A variable valve gear, comprising: a cam shaft(1); a control cam (2) mounted on said cam shaft (1); a cam follower(3); a valve (4); a valve displacing device (5) for displacing saidvalve (4); a valve lever (6) between said cam follower (3) and saidvalve displacing device (5), said valve lever (6) being swivellablycoupled to said valve displacing device (5); a control lever (8)rotatable about an axis (9) and swivallably coupled to said valve lever(6) at a swivel joint; an adjusting device (7) for displacing said axis(9) along a path; whereby the stroke of said valve (4) can becontinuously variable from a maximum to a minimum, according thedisplacement of said axis (9) along said path;
 2. A variable valve gear,as claimed in claim 1, characterized in that: said axis (9) is movableat a substantially constant distance from a fixed to said engine axis(10); thereby the stroke of said valve (4) is controlled by the angulardisplacement of said axis (9) about said fixed to said engine axis (10).3. A variable valve gear, as claimed in claim 1, characterized in that:said axis (9) is movable at a constant distance from a fixed to saidengine axis (10); said constant distance being substantially equal tothe distance between said axis (9) and the center of said swivel joint;thereby the clearance of said valve (4) can be constant, independent ofthe valve stroke of said valve (4);
 4. A variable valve gear, as claimedin claim 1, wherein: said control lever (8) has an effective lengthequal to the distance from said axis (9) to the center of the swiveljoint coupling said control lever (8) and said valve lever (6); saidvalve lever (6) has an effective length equal to the distance from thecenter of the swivel joint coupling said control lever (8) and saidvalve lever (6), to the center of the swivel joint coupling said valvelever (6) and said valve displacing device (5); characterized in that:said effective length of said control lever (8) is substantially equalto said effective length of said valve lever (6); thereby when said axis(9) is displaced at the center of said swivel joint coupling said valvelever (6) and said valve displacing device (5), the stroke of said valve(4) becomes zero.
 5. A variable valve gear, as claimed in claim 1,wherein: said control lever (8) has an effective length equal to thedistance between said axis (9) and the center of said swivel jointcoupling said control lever (8) and said valve lever (6); said valvelever (6) has an effective length equal to the distance between thecenter of said swivel joint, coupling said control lever (8) and saidvalve lever (6), and the center of the swivel joint coupling said valvelever (6) and said valve displacing device (5); characterized in that:said axis (9) moves sustaining a substantially constant distance from afixed to said engine axis (10); said effective length of said controllever (8) being substantially equal to said constant distance betweensaid axis (9) and said fixed to said engine axis (10); said effectivelength of said valve lever (6) being substantially equal to saidconstant distance between said axis (9) and said fixed to said engineaxis (10); thereby the stroke of said valve (4) can vary, according theangular displacement of said axis (9) about said fixed to said engineaxis (10), from a maximum value to zero, while said valve (4) clearanceis substantially constant for every stroke of said valve (4);
 6. Avariable valve gear, as claimed in claim 1, characterized in that: aspring element provides force for keeping said cam follower (3)substantially in contact with said control cam (2).
 7. A variable valvegear, as claimed in claim 1, characterized in that: a spring elementprovides a force for keeping said cam follower (3) substantially incontact with said control cam (2) at short valve strokes, while it idlesat long valve strokes;
 8. A variable valve gear, as claimed in claim 1,characterized in that: said adjusting device (7) controls more than onevalves.
 9. A variable valve gear, as claimed in claim 1, characterizedin that: said cam follower (3) is a roller rotatably supported to saidvalve lever (6), or to said control lever (8), or both.
 10. A variablevalve gear, as claimed in claim 1, characterized in that: said camfollower (3) is made as a cylindrical shape surface secured to saidcontrol lever (8); the center of said swivel joint coupling said controllever (8) and said valve lever (6) being substantially on the axis ofsaid cylindrical surface; said axis (9) moves sustaining a constantdistance from a fixed to said engine axis (10); said axis of saidcylindrical surface being, when said valve (4) is closed, substantiallyon said fixed to said engine axis (10); thereby the clearance of saidvalve (4) can be substantially constant as the displacement of said axis(9) varies.
 11. A variable valve gear, as claimed in claim 1,characterized in that: said cam follower (3) is mounted on said valvelever (6).
 12. A variable valve gear, as claimed in claim 1,characterized in that: said valve lever (6) being mere a push rod.
 13. Avariable valve gear as claimed in claim 1, characterized in that thereis a hydraulic member for automatic clearance compensation.
 14. Avariable valve gear as claimed in claim 1, characterized in that saidcam shaft is driven by means of a variable valve timing system in orderto control both, the stroke and the timing of the valve.